The present invention pertains to a device, and a method for placing the device, for treating a failing heart. In particular, the device and its related method of the present invention are directed toward reducing the wall stress in a failing heart. The device reduces the radius of curvature and/or alters the geometry or shape of the heart to thereby reduce wall stress in the heart and improve the heart""s pumping performance.
Heart failure is a common course for the progression of many forms of heart disease. Heart failure may be considered as the condition in which an abnormality of cardiac function is responsible for the inability of the heart to pump blood at a rate commensurate with the requirements of the metabolizing tissues, or can do so only at an abnormally elevated filling pressure. There are many specific disease processes that can lead to heart failure. Typically these processes result in dilatation of the left ventricular chamber. Etiologies that can lead to this form of failure include idiopathic, valvular, viral, and ischemic cardiomyopathies.
The process of ventricular dilatation is generally the result of chronic volume overload or specific damage to the myocardium. In a normal heart that is exposed to long term increased cardiac output requirements, for example, that of an athlete, there is an adaptive process of slight ventricular dilation and muscle myocyte hypertrophy. In this way, the heart fully compensates for the increased cardiac output requirements. With damage to the myocardium or chronic volume overload, however, there are increased requirements put on the contracting myocardium to such a level that this compensated state is never achieved and the heart continues to dilate.
The basic problem with a large dilated left ventricle is that there is a significant increase in wall tension and/or stress both during diastolic filling and during systolic contraction. In a normal heart, the adaptation of muscle hypertrophy (thickening) and ventricular dilatation maintain a fairly constant wall tension for systolic contraction. However, in a failing heart, the ongoing dilatation is greater than the hypertrophy and the result is a rising wall tension requirement for systolic contraction. This is felt to be an ongoing insult to the muscle myocyte resulting in further muscle damage. The increase in wall stress also occurs during diastolic filling. Additionally, because of the lack of cardiac output, a rise in ventricular filling pressure generally results from several physiologic mechanisms. Moreover, in diastole there is both a diameter increase and a pressure increase over normal, both contributing to higher wall stress levels. The increase in diastolic wall stress is felt to be the primary contributor to ongoing dilatation of the chamber. Prior treatments for heart failure associated with such dilatation fall into three general categories. The first being pharmacological, for example, diuretics and ACE inhibitors. The second being assist systems, for example, pumps. Finally, surgical treatments have been experimented with, which are described in more detail below.
With respect to pharmacological treatments, diuretics have been used to reduce the workload of the heart by reducing blood volume and preload. Clinically, preload is defined in several ways including left ventricular end diastolic pressure (LVEDP), or indirectly by left ventricular end diastolic volume (LVEDV). Physiologically, the preferred definition is the length of stretch of the sarcomere at end diastole. Diuretics reduce extra cellular fluid which builds in congestive heart failure patients increasing preload conditions. Nitrates, arteriolar vasodilators, angiotensin converting enzyme (ACE) inhibitors have been used to treat heart failure through the reduction of cardiac workload by reducing afterload. Afterload may be defined as the tension or stress required in the wall of the ventricle during ejection. Inotropes function to increase cardiac output by increasing the force and speed of cardiac muscle contraction. These drug therapies offer some beneficial effects but do not stop the progression of the disease.
Assist devices include mechanical pumps. Mechanical pumps reduce the load on the heart by performing all or part of the pumping function normally done by the heart. Currently, mechanical pumps are used to sustain the patient while a donor heart for transplantation becomes available for the patient.
There are at least three surgical procedures for treatment of heart failure associated with dilatation: 1) heart transplantation; 2) dynamic cardiomyoplasty; and 3) the Batista partial left ventriculectomy; and 4) the Jatene and Dor procedures for ischemic cardiomyopathy, discussed in more detail below. Heart transplantation has serious limitations including restricted availability of organs and adverse effects of immunosuppressive therapies required following heart transplantation. Cardiomyoplasty involves wrapping the heart with skeletal muscle and electrically stimulating the muscle to contract synchronously with the heart in order to help the pumping function of the heart. The Batista partial left ventriculectomy surgically remodels the left ventricle by removing a segment of the muscular wall. This procedure reduces the diameter of the dilated heart, which in turn reduces the loading of the heart. However, this extremely invasive procedure reduces muscle mass of the heart.
Another form of heart failure results from the formation of one or more zones of ischemia, or infarction, of the myocardium. Infarction occurs when blood supply to the heart tissue has been obstructed resulting in a region of tissue that loses its ability to contract (referred to as infarcted tissue). The presence of infarcted tissue may lead to three conditions in the heart causing cardiac malfunction. These conditions are ventricular aneurysms (ventricular dyskinesia), non-aneurysmal ischemic or infarcted myocardium (ventricular akinesia), and mitral regurgitation.
A ventricular aneurysm is formed when the infarction weakens the heart wall to such an extent that the tissue stretches and thins, causing, for example, the left ventricular wall to expand during systole (dyskinesia) and form a bulge in the heart wall. Non-aneurysmal ischemic or infarcted myocardium (akinesia) occurs when a major coronary artery is occluded and results in infarction in the myocardial tissue, but without a bulging aneurysm. Finally, mitral regurgitation is a condition whereby blood leaks through the mitral valve due to an improper positioning of the valve structures that causes it not to close entirely. If the infarcted or aneurysmal region is located in the vicinity of the mitral valve, geometric abnormalities may cause the mitral valve to alter its normal position and dimension, and may lead to annular dilatation and the development of mitral regurgitation.
The xe2x80x9cDorxe2x80x9d and xe2x80x9cJatenexe2x80x9d procedures have recently been employed to treat heart conditions resulting from aneurysms and other infarctions. In the xe2x80x9cDorxe2x80x9d procedure, the aneurysm is removed and an endocardial patch is placed to cover the dyskinetic septal wall portion of the aneurysm. In this manner, at least the portion of stroke volume xe2x80x9clostxe2x80x9d to dyskinesia is restored. In the xe2x80x9cJatenexe2x80x9d technique, a purse string suture is placed at the base of the aneurysm. The infarcted septal wall is circumferentially reduced by inbrication with sutures.
The advantages and purpose of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
Due to the drawbacks and limitations of the previous devices and techniques for treating a failing heart, including such a heart having dilated, infarcted, and/or aneurysmal tissue, there exists a need for alternative methods and devices that are less invasive, pose less risk to the patient, and are likely to prove more clinically effective. The present invention provides such methods and devices.
Although throughout this specification, the inventive devices and methods will be discussed in connection with treating dilated heart chambers, it is contemplated that the form of heart failure resulting from aneurysms and the like also can be treated with the inventive device and method for using the device disclosed herein. U.S. application Ser. No. 09/422,328, filed on Oct. 21, 1999, entitled xe2x80x9cMethods and Devices for Improving Cardiac Function in Hearts,xe2x80x9d which is assigned to the same assignee as the present application and is incorporated by reference herein, discusses this form of heart failure in more detail.
One aspect of the present invention pertains to a non-pharmacological, passive apparatus and method for the treatment of a failing heart due to dilatation. The device is configured to reduce the tension in the heart wall, and thereby reverse, stop or slow the disease process of a failing heart as it reduces the energy consumption of the failing heart, decreases isovolumetric contraction, increases isotonic contraction (sarcomere shortening), which in turn increases stroke volume.
The device reduces wall tension by changing chamber geometry or shape and/or changing the radius of curvature or cross-section of a heart chamber. These changes may occur during the entire cardiac cycle. The apparatuses of the present invention which reduce heart wall stress in this way can be referred to generally as xe2x80x9csplints.xe2x80x9d Splints can be grouped as either xe2x80x9cfull cycle splints,xe2x80x9d which engage the heart to produce these changes throughout the cardiac cycle, or xe2x80x9crestrictive splints,xe2x80x9d which engage the heart wall for only a portion of the cardiac cycle to produce these changes.
One aspect of the present invention includes an apparatus for improving cardiac function includes an elongate member configured to extend transverse a heart chamber, a first heart-engaging assembly attached to one end of the elongate member and configured to engage a first exterior location of a heart wall, and a second heart-engaging assembly configured to be secured onto the elongate member and to engage a second exterior location of the heart wall. The apparatus further includes a fixation member configured to penetrate the elongate member to thereby hold at least one of the first and second heart-engaging assemblies in a fixed position along the length of the elongate member.
According to another aspect of the present invention, an apparatus for improving cardiac function includes an elongate member configured to extend transverse a heart chamber, wherein the elongate member is made of a plurality of filament bundles of approximately 180 denier. The apparatus further includes a first heart-engaging assembly attached to one end of the elongate member and configured to engage a first exterior location of a heart wall and a second hear-tengaging assembly configured to be secured onto the elongate member and to engage a second exterior location of the heart wall.
According to yet another aspect of the present invention an apparatus for improving cardiac function includes an elongate member attached to a leader member at one end thereof and being configured to extend transverse a heart chamber, a first heart-engaging assembly attached to the other end of the elongate member and configured to engage a first exterior location of a heart wall, and a second heart-engaging assembly configured to slidably receive the leader member and the elongate member and to thereby be secured to the elongate member and to engage a second exterior location of the heart wall. The second heart-engaging assembly is configured to be secured to the elongate member such that a length of the elongate member between the first and second heart-engaging assemblies can be adjusted during placement of the elongate member transverse the heart chamber.
Another embodiment of the present invention includes an apparatus is provided for determining and marking locations on a heart wall. The apparatus includes a marker delivery mechanism configured to hold a marker and an actuator operatively connected to the marker delivery mechanism for delivering a marker to the location. The distal end of the delivery mechanism is configured to be visible relative to internal heart structures.
Yet another embodiment of the present invention includes a tool for fixing an elongate member to a housing comprising an engagement member configured to engage a fixation member to be advanced within the housing, a wire having a first end secured to the engagement member and being configured to pass through the housing, and a handle connected to a second end of the wire. The engagement member and the wire are further configured to move through the housing to advance the fixation member within the housing and into engagement with the elongate member when the handle is actuated.
In another embodiment of the present invention, there is provided a method for placing a splint assembly transverse a heart chamber. The method includes providing an elongate member with a leader member attached to a first end and a first heart-engaging assembly attached to a second end and guiding the leader member through first and second exterior locations on a heart wall so as to extend the elongate member transverse to the heart chamber. The method further includes adjusting the length of the elongate member extending through the heart chamber by securing a second heart-engaging assembly to the elongate member at a position along the length of the elongate member exterior the chamber at the second location.
In accordance with the purposes of the invention as embodied and broadly described herein, instruments and related methods for implanting the device for treating a heart and improving cardiac function also are disclosed.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.